Wednesday, August 19, 2009

r/K selection at the national level

The r/K selection theory, coined by E. O. Wilson, concerns the trade off between the quantity of offspring produced and the quality of care and devotion given to each of them. From the Wikipedia article:

r-selected species exploit less-crowded ecological niches, and produce many offspring, each of which has a relatively low probability of surviving to adulthood. In contrast, K-selected species are strong competitors in crowded niches, and invest more heavily in fewer offspring, each of which has a relatively high probability of surviving to adulthood.

In this conceptual framework, humans are clearly a K-selected species. Frogs and spiders, in contrast, are examples of r-selected species.

Intraspecies differences exist as well. In Race, Evolution, and Behavior, Philippe Rushton describes human populations as existing along an r/K continuum, with blacks nearest the r side, Asians nearest the K side, and whites in between.

My purpose is not to detract from or defend that conceptualization, but instead to present the relationship between fecundity and infant mortality at the national level. The following graph depicts this, with the total fertility rate along the x-axis and infant mortality per 1,000 live births on the y-axis:

The correlation between the two is .83 (p=0), very strong for the social sciences. This does not imply that the causes of national differences are primarily genetic in nature. Over the last 60 years, the infant mortality rate in the US has nearly been cut in half while the birth rate has declined by more than one-third over the same period of time. For American blacks, the infant mortality rate is 13.6, compared to 44.4 for the entire country of South Africa, the most developed nation in sub-Saharan Africa.

11 comments:

Philippe Rushton describes human populations as existing along an r/K continuum, with blacks nearest the r side, Asians nearest the K side, and whites in between.

I'm inclined to believe Rushton is wrong about r/K being variable across races.

Ruston's r/K continuum is only true if you look at current fertility rates.

However, if you look at European and Asian civilizations between 1000 B.C. and 1800 A.D., NEAsians and Europeans had at least as many offspring as African tribes did.

In fact, our current situation of wealth combined with lower fertility is unique because, historically, wealthy and peaceful periods were associated with very high fertility rates i.e Europe during the Medieval ages and Renaissance and Colonial America, which was one of the wealthiest areas of the world in the 18th century (the colonial white American fertility rate has been estimated at being around 7.0 - higher than modern African birthrates and higher than much of 18th century Europe).

It appears that Europeans and Asians can, under the right circumstances, have very high birthrates combined with high levels of investiture for raising children.

Africans have the potential for high fertility but also very low investment in human capital.

2) as noted above, historically birhrates were all over the map. the main determinant of fertility was probably resources in a malthusian context. highest recoded fertility was in 17th century mass. colony in he USA, puritans on the frontier. 12 children per woman.

That is very strong support for the human population as a whole being sensitive to the r/K scale (as I understand it) in the sense that downward birthrate adjustments are made when the difficulty of survival decreases in human society.

The race thing is plausible but if it exists at all I would suspect that its effect is very small compared with the effects of the environment at large. It's difficult to control for environment too since, as you point out, even within a nation infant mortality rates can vary among groups.

if you look at European and Asian civilizations between 1000 B.C. and 1800 A.D., NEAsians and Europeans had at least as many offspring as African tribes did.

This is the case, with certainty? A TFR difference of .5, say 6.5 in Renaissance Europe and 7 in Africa at the same time would still fit. I'm obviously ignorant of the actual numbers though (Razib might know), but am inclined towards Jokah's view that there are slight human population differences (differences in premature birth rates, speed of infant development, infant mortality rates, etc), but that they are swamped and obscured by more influential environmental/cultural factors.

A TFR difference of .5, say 6.5 in Renaissance Europe and 7 in Africa at the same time would still fit.

The best one could say of Rushton's theory in this case would be that there is possibly some small genetic racial variation in r/K continuum but that the phenomenon is totally dwarfed by cultural and environmental variables.

Environment and cultural factors such as the birth control pill, women's labor force participation rates and the amount of years in school would still be far more important than r/K genetic variation across races.

Until antibiotic campaigns in the 1960s much of Africa was affected by venereal infertility. Fertility especially in Central Africa shot way up toward the end of the 1960s. Such historical accidents make large scale generalizations iffy.

Re r-K theory--it is a nice tune but never was turned into a real theory with falsifiable predictions. It retains its place as a kind if heuristic but not serious theory.